Logic is usually thought to concern itself only with features that sentences and arguments possess in virtue of their logical structures or forms. The logical form of a sentence or argument is determined by its syntactic or semantic structure and by the placement of certain expressions called “logical constants.”[1] Thus, for example, the sentences Every boy loves some girl. and Some boy loves every girl. are thought to differ in logical form, even though they share a common syntactic and semantic (...) structure, because they differ in the placement of the logical constants “every” and “some”. By contrast, the sentences Every girl loves some boy. and Every boy loves some girl. are thought to have the same logical form, because “girl” and “boy” are not logical constants. Thus, in order to settle questions about logical form, and ultimately about which arguments are logically valid and which sentences logically true, we must distinguish the “logical constants” of a language from its nonlogical expressions. (shrink)

Greek antiquity saw the development of two distinct systems of logic: Aristotle’s theory of the categorical syllogism and the Stoic theory of the hypothetical syllogism. Some ancient logicians argued that hypothetical syllogistic is more fundamental than categorical syllogistic on the grounds that the latter relies on modes of propositional reasoning such asreductio ad absurdum. Peripatetic logicians, by contrast, sought to establish the priority of categorical over hypothetical syllogistic by reducing various modes of propositional reasoning to categorical form. In the 17th (...) century, this Peripatetic program of reducing hypothetical to categorical logic was championed by Gottfried Wilhelm Leibniz. In an essay titledSpecimina calculi rationalis, Leibniz develops a theory of propositional terms that allows him to derive the rule ofreductio ad absurdumin a purely categorical calculus in which every proposition is of the formA is B. We reconstruct Leibniz’s categorical calculus and show that it is strong enough to establish not only the rule ofreductio ad absurdum, but all the laws of classical propositional logic. Moreover, we show that the propositional logic generated by the nonmonotonic variant of Leibniz’s categorical calculus is a natural system of relevance logic known as RMI$_{{}_ \to ^\neg }$. (shrink)

Logic, an old discipline with a long history, is a product of the nature of thinking that is based on mental thought, which is distinguished from other creatures by human nature. Logical thought and various forms of rational inference, seen in all the geographical regions of the world before attaining a systematic structure, have directed to human life and its scientific products. A systematic structure is taken back to Parmenides, lived in ancient Greek thought. The logic developed from various directions (...) was given a proper shape by Aristotle nearly two thousand years ago and has been in continuous development and transformation in the direction of human mind and its needs. Today, in addition to Aristotelian logic, which is two most valuable structures, many valued logics have emerged.. Quite different logic conception emerges from classical logic, however, which is considered as a beginning for philosophical thought and is one of the important factors in reaching the goal of the philosophical effort. But the presence of classical logic continues in the areas of religious, classical philosophy and social sciences. In this frame, the value of classical logic from past histories requires the position that it deserves. Especially, in the area of logic as well as the problems faced in logic education, more effective planning is required especially in the higher education level. This article will briefly discuss the structure of logic and its various interpretations. It will also point out the importance of logic and will draw attention to the problems in the Theology Faculties. A few suggestions that we want to discuss in this framework will also be put forward. (shrink)